The present invention is directed to a corrective eyeglass lens, and, in particular, to an eyeglass lens which corrects astigmatism, hyperopia, myopia and the like.
Corrective eyeglass lenses known in the art have a structure such as eyeglass lens 10 shown in FIG. 1. Eyeglass lens 10 has a front refracting surface 12 which is spherical and a back refracting surface 14 which may be formed as a spherical or a non-spherical surface known as the toric surface which is adapted to the prescription of the eyeglass wearer. Distortions arise in the visual image passing through lens 10 in the form of astigmatism. The astigmatism of lens 10 is illustrated in FIG. 2 and can be reduced by selecting a value of the radius of curvature for the spherical surface of front refracting surface 12. However, in a conventional lens, the radius of curvature of front refracting surface 12 is most likely relatively small, resulting in a forward protrusion which is rather conspicuous and detracts from the aesthetic value of the eyeglass lens. Additionally, such a lens construction does not lend itself to reduction in eyeglass thickness or weight.
Reference is now made to FIGS. 3 and 4 in which an eyeglass lens 20, constructed in accordance with the prior art, includes a front refracting surface 22 formed as a non-spherical surface, symmetric with respect to the rotation axis R through the center O of lens 20. The forward protrusion of lens 20 has been reduced while retaining the distortion at a lowest possible level, achieving a substantial improvement in terms of thickness and weight as well as aesthetics. The distortions are mitigated by forming the forward refracting surface 22 as a non-spherical surface. Lens 20 has been satisfactory. However, if the distortions are mitigated, these distortions are only mitigated with respect to an object positioned at a fixed distance and not over a range of distances.
As can be seen from FIG. 4, there is no decrease in the astigmatism with respect to objects at other distances from the closest vicinity represented by 0.3 meters to a long distance represented by infinity. Lens 20 provides a clear visual field with little astigmatism with respect to an object at a position 1 meter away. However, with respect to the other distances, there is not a complete elimination of the astigmatism.
Accordingly, it is desired to provide an eyeglass lens which overcomes the shortcomings of the prior art.